You've heard they can turn back the clock on aging skin -- products made with things like acai, alpha-lipoic acid, and alpha-hydroxy acid.

But do they work? Can they actually erase wrinkles, repair sun damage, or fade age spots?

Before you buy, it’s a good idea to learn more about these ingredients. A dermatologist can also help you sort out what works, what's hype, and what might help your skin.

Antioxidants for Sun Damage and Wrinkles

Most plants have these nutrients in varying amounts. They can counter "free radicals," tiny particles that harm DNA inside of cells. Skin cells with that kind of damage can speed up aging, leading to wrinkles, dry skin, dark circles under eyes, dull skin, and more.

Foods that are rich in antioxidants are good for your skin and your overall health. You can also apply products that have them. Those with the most antioxidants that have been shown to repair damage and slow the aging process include:

Alpha-Lipoic Acid

Your body makes this natural chemical, and it’s in every cell you have. As an antioxidant, it attacks free radicals throughout the body. In skin care products, companies tout it as a substance that can erase fine lines and wrinkles, diminish pores, and give skin a healthy glow.

Green Tea Extract

Tea is loaded with nutrients called polyphenols, which have been shown to fight free radicals.

Early studies have found the ingredients in tea can ease sun damage and may protect you from skin cancer when you put it on your skin. Use green tea extract under sunscreen to double the protection. Polyphenols in creams and lotions may also slow signs of aging and reduce sagging skin and wrinkles.

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Retinol

Made from vitamin A, retinol is added to creams that go on your skin. It boosts the amount of collagen your body makes and plumps out skin, reducing fine lines and wrinkles. It also improves skin tone and color and reduces mottled patches.

Many dermatologists prescribe retinol's stronger counterpart, tretinoin, or similar products, to slow skin aging, improve irregular coloring, and clear up acne. Over-the-counter products that have retinols may be weaker, but they can still improve how your skin looks.

Using a retinol-based product may make the top layer of your skin dry and flaky. It’s best to apply it at night and wear moisturizer and sunscreen the next morning, or ask your dermatologist about alternatives.

Vitamin C

As you age, your body makes less collagen and elastin, which keep skin strong, flexible, and resilient. The antioxidants in vitamin C may boost the amount of collagen and minimize fine lines, wrinkles, and scars.

Vitamin C is in some skin care products such as creams and lotions. If you want to try one, ask your dermatologist for some options.

Coenzyme Q-10 (CoQ-10)

Your body naturally makes this antioxidant to zap free radicals in cells. As you age, you make less. That may make skin cells more vulnerable to damage. That's the reason it’s in skin care products such as toners, gels, and creams, which you can use on their own or with a moisturizer. One study shows that CoQ10 helps reduce “crow’s feet,” the wrinkles around the eyes.

Caffeine

It's also an antioxidant, but experts don't know whether it can reverse aging on your skin. Still, companies have added it to lotions and creams based on research that shows caffeine could help prevent the growth of skin cancer and, when applied to the skin, may make wrinkles less defined, especially ''crow's feet'' around the eyes.

Other Popular Ingredients

When you shop for makeup and skin care products, you may see other ingredients on their labels:

Alpha-hydroxy Acids (AHAs)

This group includes glycolic, lactic, citric, and tartaric acids. They’re in many products.

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They exfoliate the skin, reducing fine lines, age spots, acne scars, and uneven skin color. You can get peels with high concentrations of AHAs from a beauty specialist (esthetician) or dermatologist, but you can use lower concentrations -- between 5% and 10% -- in creams or lotions on a daily basis.

Start with a low concentration and apply every other day to avoid irritating your skin. Over time, you can gradually start to use it more often, working up to every day.

Even at lower doses, though, the acids may irritate and dry skin, and make it more sensitive to the sun. Doctors recommend using moisturizer and sunscreen when you use any products that have AHAs.

Salicylic Acid

You’ll see this ingredient in many over-the-counter and prescription products that treat acne. It penetrates pores and reduces blackheads and whiteheads with less irritation than what you might get from alpha-hydroxy acids. Like AHAs, salicylic acid exfoliates the skin, which can reduce signs of aging.

You shouldn't use salicylic acid if you are allergic to aspirin or other products with salicylates. If you’re pregnant or nursing, ask your doctor before you use any product with salicylic acid. Stop using the product if you get hives or itching. Also, be aware of symptoms of rare but serious allergic reactions -- throat tightness, trouble breathing, feeling faint, or swelling of your face or tongue. Get help right away if you have these problems.

Hyaluronic Acid

Your body makes hyaluronic acid naturally, keeping tissues cushioned and lubricated. It's found in skin, joint fluid, and connective tissues. Age, smoking, and an unhealthy diet can cause you to make less of it over time.

Products that have hyaluronic acid may help smooth out skin. They work especially well when you use them with vitamin C products.